The present invention relates to a new and improved construction of a filling-thread insertion element for looms working with removal of the filling thread from stationary bobbins or spools. The filling-thread insertion element of the invention is of the type comprising a flexible insertion band or tape, a gripper driven by such insertion band, this gripper being provided with a clamp element or clamp for fixedly clamping the filling or weft thread, and with a reinforcement element arranged at the insertion band at its region merging with the gripper.
With state-of-the-art band gripper looms of this type there is arranged to both sides of the loom a respective band or tape wheel, at which there is secured the respective end of an insertion band or tape. At the other end of each insertion band there is mounted a gripper for the insertion of the filling threads. The insertion bands are oscillatingly driven by the band wheels, and thus, are continuously and alternately wound-up and wound-off the band wheels. Thus, particularly at the region of attachment locations of the gripper with the insertion bands there arise bending loads which are predicated upon flutter or oscillatory movements of the gripper heads, and these bending loads can lead to rupture.
To reduce the danger of such rupture and for stabilizing the gripper travel or operation, it has already been proposed to provide the insertion bands with a reinforcement at their end supporting the gripper. One such prior art solution resides in providing the insertion bands, at the aforementioned end, with a transverse domed or arched portion, and according to another known solution the insertion bands are uniformly connected at their end region with a reinforcement strip.
Practical tests undertaken on equipment designed according to these proposals have shown that these solutions have not been capable of completely eliminating the flutter movements of the equipment, and furthermore, the aforementioned rupture or fracture still occurs. Additionally, it has been found that with increasing frequency of the filling-thread insertion operations the grippers are deflected at the reversal points of their movement out of their horizontal path of travel. At the outer reversal of turning point, in other words at the start of a filling-thread insertion, the grippers are pressed upwardly at an inclination away from their path of travel and at their inner reversal or turning point they are downwardly pressed. As a result, in the first mentioned case the grippers contact the warp threads at the upper shed and damage the same and, due to the action of these warp threads, the grippers are in fact even displaced out of the shed, whereas in the last-mentioned case both of the grippers which have been displaced within one another or interengaged can damage one another.
The attachment of the grippers at their insertion band is accomplished with the heretofore known gripper looms, in most instances, by soldering, but in a number of cases by thread connections or screws. Soldering requires a great amount of work and places extreme demands upon the precision of the workers or operating personnel. On the other hand, the local heating of the gripper and the insertion band, caused by the soldering operation, often results in distortion of the insertion band, which cannot or only with great difficulty be eliminated by performing a subsequent straightening or correction operation.
As to the economical operation of a loom, for a given weaving or cloth weave, the number of filling-thread insertions per minute, the so-called number of revolutions, is of decisive importance. The number of revolutions, in the case of band gripper looms, among other things, is limited by the relatively large mass of the grippers. This mass heretofore only could be slightly reduced, because the material used for the grippers, owing to the requirement that it be capable of being soldered with the insertion band or tape formed of steel, practically likewise was limited to steel.
The screwing or threading together of the gripper with the insertion bands was not heretofore accepted practice because, on the one hand, such type of screw connection did not have the requisite stability, and, on the other hand, the insertion bands at the region of the rather limited anchoring locations of the screws, generally only one but at most two anchoring locations of the screws, were exposed to an excessive wear.